[codex] Add market benchmark evidence

[RollNuts]

What changed

Adds docs/MARKET_BENCHMARK_2026-06-29.md, a Steam-facing market benchmark for Cinder Ward.

The document covers:

• 10 benchmark games.
• Steam official screenshot/movie counts from appdetails.
• Local visual observations from representative Steam-hosted screenshots.
• Specific implications for Cinder Ward's first character, room readability, pressure loop, and avoid list.

Why

The project needs a stronger direction grounded in actual Steam visuals, trailers, and replay hooks, not just text descriptions. This PR gives the art/gameplay work a benchmark-backed target before more assets are produced.

Validation

• Checked the added document for secret-like strings with rg.
• Pulled Steam official media metadata for the 10 benchmark apps.
• Downloaded representative Steam-hosted screenshots locally for visual inspection; no third-party media is committed.

Merge notes

This PR is documentation-only. It can merge after the repo policy self-match fix because current main policy still flags scanner configuration text on unrelated PRs.

[RollNuts]

Veripsa triage request: include this market benchmark PR in the merge-order set with #13, #8, #9, #10, #11, #12, #15, and #16.

Expected ordering note: #13 should likely merge first because current main policy self-matches scanner configuration and causes unrelated docs PRs to fail repo-policy / validate. After that, this PR can inform #15 game direction, #9 protagonist target, #10 pressure loop, and #16 audio direction.